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  • 1 INQUINOA—CONICET. Instituto de Química Orgánica. Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, CP T 4000 INI, Tucumán, Argentina
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Abstract

A method to determine soil microbial biomass (SMB) by isothermal calorimetry is reported. Soil samples ranging in pH from 6.2 to 9.4 and different textures were used to develop the method. Soil at 60% of its field capacity humidity was amended with a previously determined amount of glucose as to give the maximal response of CO2 evolution. Then, an aliquot was weighed in the calorimeter ampoule and specific thermal power (p)–time (t) curves were obtained at 25 °C. After 1–2 h, a vial containing a 0.5 M NaOH solution was introduced to determine the specific thermal power due to CO2 evolution, pCO2 during 1–2 h. Then, the vial was removed and the experiment continued for 1–2 h. Specific thermal power due to CO2 evolution was converted to rate (CO2-C/mm3 g−1 h−1) by using the heat of reaction of CO2 with NaOH and the molar volume. This value was further converted into SMB/μg g−1 by using a conversion factor of 32.4. A guide to perform the calculations is given. Values of log SMB were linearly related with values of log p giving a similar relation to a previously reported where SMB was determined by conventional methods.

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